The investigators hypothesize that daytime sequela of sleep apnea such as excessive daytime sleepiness and cognitive dysfunction are the result of subtle deficits in brain metabolism due to hypoxemia and resultant carbon dioxide retention. They aim to characterize and localize the abnormalities of the brain through topographic EEG mapping and evoked potentials; assess the permanence of brain dysfunction and correlate the daytime symptoms with electrophysical abnormalities through objectives, electrophysiological and neurophysiological measures.